Photothermal microscopy for in-situ study of laser interaction with 100-nm-diameter gold nanoparticles embedded in silica thin films

摘要

In the context of high power laser applications, laser-induced-damage in fused silica is still a limitation which need more study. To obtain better understanding of induced-breakdown processes, pure silica "model" samples, seeded with 100-250 nm diameter gold nanoparticles have been prepared. The aim in using these samples is to observe the mechanism of damage initiation that can be attributed to inclusions of nano-metric size. These samples were studied in a series of experiments using a photothermal microscope coupled with an experimental set-up allowing damage threshold measurement at wavelength 1064 nm. This installation is of great interest because it enables us to combine the laser irradiation of the sample with the optical absorption measurement. An evaluation of the silica transformation as a function of the fluence of irradiation can thus be obtained from the experimental results. These experimental data are completed with "Nomarski" and "atomic force" microscope observations, and then interpreted. Finally, we compare our results to numerical simulations performed with a 1-D hydrodynamic code. These simulations indicate that the threshold for melting the gold inclusion as a function of the incident laser fluence exceeds the threshold at which the absorption of the inclusion decreases.